As global air traffic has continued to grow overthe past two decades, it has effectively led to a sharp increase in the emissions and corresponding global warming through the 'greenhouse gas effect'. Apart from CO₂ and H₂O, NO_x is the next major aviation-emitted species which significantly contributes to climatechange through its atmospheric chemistry leading to the formation of O₃,which in itself is another major greenhouse gas. 

Since global air traffic is a major source of tropospheric NO_x,this thesis analyzed the contribution of aviation to tropospheric mixing ratiosof NO_x and O₃. The analyses were performed on 2 majoraspects: (A) to identify and understand the seasonal & zonal patterns with respect to aviation's contribution to tropospheric mixing ratio of NO_x andO₃, and (B) to comprehend the differences between 2 methodologies(called “Perturbation” & “Tagging”) in estimating aviation's contributionto tropospheric mixing ratio of NO_x and O₃. Inaddition to NO_x and O₃, background availability ofradicals OH and HO₂ was also analyzed, since OH and HO₂ arevital to the NO_x-O₃ chemistry.

The global climate-chemistry model EMAC (European Centre forMedium-Range Weather Forecasts – Hamburg (ECHAM)/MESSy Atmospheric Chemistry) was used, whereby the simulations were performed in quasi-chemistry transport model (QCTM) mode. The analyses presented an interesting overview of aviation's contribution to tropospheric NO_x and O₃.